The present invention relates, in general, to an electric machine with a laminated rotor core
An electric machine of a type typically involved here includes a rotor having a rotor core which is mounted onto a shaft and formed of a plurality of stacked laminations. The rotor core carries the winding in the form of rotor bars in slots about its outer periphery, whereby the bars are connected to conducting end rings on each end. The laminated stack is provided at its end surfaces with plates that have a same cross section as the laminations of the rotor core. The plates are made of a material which is different as, e.g. the rotor bars of a squirrel-cage rotor. In view of the different materials, an aluminum cage shrinks twice as much as the surrounding lamination stack, after, e.g., a casting process. As a consequence, in particular the area of the end rings is exposed to substantial forces that tend to compress the laminated stack toward the center. When the plates, except for the slots, have a same geometry as the laminations, the end surfaces of the laminated stack undergo a constriction of the shaft bore because an axial movement of the laminations is substantially prevented.
Without the provision of special measures, it is impossible to place the shaft into the laminated stack because the necessary axial joining force to be applied in order to realize the connection becomes too great. In addition, an excessive local overmeasure may also lead to a “seizing” upon the shaft, leading to damage of the components and the rotor and ultimately to their destruction.
It would therefore be desirable and advantageous to provide an improved electric machine to obviate prior art shortcomings and to enable a compact construction of the laminated rotor core while still allowing an axial movement of the laminated stack during manufacture and simplifying the manufacture.